How does a bump key work?

Posted by Taylor Banks on June 20, 2012

What is a bump key, and how does a bump key work?

Bump keys are special keys cut to take advantage of the mechanics of pin tumbler locks and are used by first responders, security professionals, ethical hackers and social engineers to gain entry when lock picks are unavailable or impractical.*

Researchers estimate that over 95% of conventional home and business locks are vulnerable to a bump key attack. It should be noted, however, that the use of bump keys is not undetectable (as originally thought), and the use of bump keys can lead to permanent damage to a lock (depending on the lock, the force applied, and the frequency of lock bumping attempts).

Pin Tumbler Locks

To understand how bump keys function, you should first understand how a pin tumbler lock works. Pin tumbler locks contain key pins and driver pins, located within the core and cylinder, respectively. In a locked position, the key pins and driver pins occupy the same pin hole and are pushed together by a spring, preventing rotation of the core.

Aligning these pins to allow the separation between the key pin and the driver pin to align with the separation between the core and housing creates a "shear line," which allows the core or plug to rotate within the lock cylinder.

When you insert a correctly cut key into the keyway, the key pushes the pins into alignment along the shear line (by aligning the gaps between the pins with the edge of the lock core), thus allowing you to rotate the core and retract or unlock any bolt-work, ultimately allowing you to pull open the door.

If you insert the wrong key, the gap between the pins does not line up with the gap around the core, thus preventing the formation of the shear line and preventing you from rotating the core.

How to Use a Bump Key

Before you run out and buy our biggest bump key set, you should first understand how to use bump keys. While it's not hard to learn how to use bump keys, understanding their method of operation will definitely increase your chances of success with lock bumping.

A bump key is specially cut with low peaks and wide valleys that are not designed to properly align with the key pins, but instead to ensure that under force, the pins can merely be impacted.

A typical bump key is partially inserted into a lock so that one pin or notch remains between it and full insertion. Alternately, with a minimal movement bump key, the key is fully inserted and relies on the spring tension on the pins themselves to align the bump key.

The lock bumper then applies an impact force or "bump" to force the key deeper into the lock. This causes the key pins to jar and the driver pins to "jump" for a fraction of a second (much like the action demonstrated by a Newton's Cradle), aligning to create the shear line and allowing the attacker just enough time to quickly turn the core and open the lock.

How to Make a Bump Key

For the amateur locksmith or lock bumper, bump keys can be made at home (although it can be quite difficult to make a bump key properly with just a file), and they must be made from a key that already fits a particular type of lock or keyway.

Lock Picking vs. Lock Bumping

Although lock picks used skillfully do little or no damage to well-manufactured locks, such skill generally takes a significant investment of time and energy invested in lock picking practice. Bump keys, on the other hand, can be used with very little practice and yet still have a very high rate of success.

Under forensic examination, however, it is frequently quite easy to determine that a lock has been opened using lock bumping techniques.

How We Use Bump Keys

In summary, although we often prefer picking locks to bumping them on an engagement (remember, bump keys can generate quite a disturbance when used in a public setting), bump keys are very useful for demonstrating attacks against a variety of modern locks and the ease with which a lock can be opened even without extensive training or practice. Furthermore, you can make a bump key with just a few tools and a proper understanding of their operation.

Want to try your hand at lock bumping, but don't want to take the time to make your own bump keys? ACE Hackware manufactures the highest quality bump keys available. Remember, though, because bump keys can do damage to a lock, we highly recommend testing them on a clear practice lock, or another lock that is not in use.

Note: Breaking and entering is illegal. This information in this bump key guide is meant for educational purposes and lawful use only.

*Big thanks to scorche for lending his considerable expertise and offering suggestions and corrections!